While the operating frequency of CPUs in computer systems is increasing and the performance thereof is improving, an increase in power consumption and heat generation caused by the CPU becomes a problem. In particular, this problem is serious in the case of a CPU of a server that processes a large amount of data.
Examples of known methods of controlling the power level of a CPU include CPU throttling (frequency switching) and operating-voltage switching. Another example is a standardized method of controlling these items using advanced configuration and power interface (ACPI). In general, throughput of a CPU reduces with a reduction in the power level, so it is not good to simply reduce the power level, except when, for example, the CPU is in a standby state.
Proposed approaches to controlling the power level of a CPU include: a method of driving a fan for cooling a CPU in response to an operation from a user and turning on a throttling function of the CPU (Japanese Unexamined Patent Application Publication No. 2007-66073); and a method of changing the operating speed of a CPU in accordance with the amount of unprocessed messages (Japanese Unexamined Patent Application Publication No. 2000-194436). However, these methods are not proactive because they are countermeasures taken after the temperature of the CPU rises or the amount of unprocessed messages becomes large. Another disclosed approach is a method of automatically changing the power of a CPU while monitoring an asynchronous bus cycle to a peripheral device (Japanese Unexamined Patent Application Publication No. 9-97128). However, this approach merely reduces the power of the CPU or stops the operation thereof.